Earthworms are commonly used to test how harmful chemicals in soil can be. Scientists often use Eisenia fetida/andrei earthworms for these tests because they are easy to raise in labs and there is a lot of information on how different chemicals affect them. Tests look at things like death rates, changes in size, reproduction, and behavior. A new test is being developed to see if earthworms like or avoid certain soils. Some studies suggest that a quick test using neutral red can show how harmful heavy metals are to earthworms. The way earthworms take in, store, and get rid of metals is a big part of how toxic they are. The type of soil and how metals move in it can also affect how harmful they are to earthworms. Scientists are working on ways to predict how much metal will build up in soil and how toxic it will be to earthworms.